The present invention relates to a process for treating metal sulfides such as copper concentrates containing chalcopyrite and pyrite for rendering copper and iron values amenable to selective leaching and separate recovery.
It is known to heat metal sulfide concentrates to remove labile sulfur and to activate the sulfide mineral mixture whereby a major portion of sulfidic iron can be leached from the said mixture permitting subsequent leaching of copper values substantially free of iron values. U.S. Pat. No. 3,053,651 discloses such a process wherein sulfide mixtures containing iron are heated to liberate labile sulfur and wherein a predetermined amount of metallic iron to provide a sulfur to iron mol ratio of less than 1:1 is added to the residual hot solids and agitated therewith in the presence of a reducing gas such as hydrogen until all of the iron content is capable of dissolution in sulfuric acid. The metallic iron may be added in the form of iron oxide produced in situ and reduced to its metallic state.
U.S. Pat. No. 3,857,767 discloses a process for recovery of copper from chalcopyrite ore concentrates in which the concentrates are partially roasted in a fluidized bed under controlled oxidizing conditions whereby excessive oxidation resulting in the formation of iron oxides such as hematite and magnetite which catalyze conversion of copper compounds to soluble copper sulfate is to be avoided. Roasting of the concentrates thus is to be terminated prior to formation of the iron oxides.
It is taught in U.S. Pat. No. 3,964,901 that copper-containing pyritic metal sulfides can be thermally activated for preferential selective leaching of iron values from copper values by heating said sulfides sequentially in a reactor in an effectively non-oxidizing atmosphere and then in a reducing atmosphere for liberation of labile sulfur and controlled combustion of said labile sulfur and any combustible gases by the addition of a limited amount of an oxygen-containing gas to maintain a desired reactor temperature in said non-oxidizing atmosphere and achieve reduction of the delabilized sulfides without formation of metal oxides whereby the pyritic iron is converted to an acid leachable form.